| Term | Description |
| Octofoil | A double quartrefoil: a leaf of eight points. When used as a difference it denotes the eighth son |
| Ogress | A black ball or pellet |
| Onde, Obdy | Wavy; curved and recurved like waves |
| Orb | A globe encircled, bearing a cross; a mound |
| Orle | 1. One of the subordinaries; in the form of a fillet, within the border, but some distance from it. 2. The wreath or chaplet surmounting or encircling the helmet of a knight and bearing the crest. IN ORLE - Said when the charges are placed round the escutcheon, leaving the middle of the field vacant, or occupied by something else. (Said of bearings arranged on the shield in the form of an orle.) |
| Overt | Applied to the wings of a bird, etc., when spread open on each side of its head , as if taking flight. |